Rocio viral encephalitis
Rocio viral encephalitis is an endemic flavivirus encephalitis that appeared in the Ribeira Valley, located on the south coast of São Paulo, Brazil, between 1975-1976.
Epidemiology
Rocio virus was first isolated from central nervous system tissue of a deceased 39-year-old male in the Rocio district of São Paulo, with serological prevalence in affected individuals confirming that this virus was the causative agent of the endemic encephalitis . The vector was later found to be a pool of Psorophora ferox mosquitoes .
Despite there being no further outbreaks of Rocio viral encephalitis, significant seroprevalence of the virus in numerous regions within Brazil threatens reemergence .
Clinical presentation
Fever, nausea, malaise, severe headache and photophobia precede features of encephalitis . Death may occur 5 days following onset of symptoms.
Pathology
Etiology
Rocio virus demonstrated a predilection for grey matter structures . Thalamic inflammatory necrosis was common . In addition, damage to the dentate nuclei, substantia inominata, brain stem, spinal cord and basal nuclei was reported .
Radiographic features
The epidemic unfortunately predates the invention of MRI, which is the modality of choice for imaging encephalitis.
Treatment and prognosis
Treatment is supportive; no vaccine is available. Mortality is approximated at 13% - 900 infected individuals and 117 deaths reported following the epidemic . Around 20% of those who survived suffer permanent neurological deficits .
Cross-protective immunity to other flaviviruses, namely Ilheus virus and Saint Louis encephalitis virus, may be a protective factor against the development of Rocio viral encephalitis .
Differential diagnosis
The Rocio viral encephalitis outbreak was unprecedented. One of the many flavivirus encephalitides would be high on the list of differentials if Rocio virus were to surface again, particularly those endemic to the Americas:
Other CNS infections are, of course, worth thinking about, for example:
- herpes simplex encephalitis
- bacteria meningitis
- fungal meningitis
- HIV CNS manifestations
- rabies encephalitis
Thorough history-taking is fundamental to establishing an appropriate list of differential diagnoses.
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